1. Field of the Invention
The present invention relates to an undercoat solution suitable for forming images, an ink-jet recording method and an ink-jet recording device.
2. Description of the Related Art
The ink-jet recording system in which ink is discharged from an discharge hole in the form of droplets, has been employed in many printers for the reasons that the printer can be small and inexpensive, image formation is possible without contacting with recording media, and the like. Among these ink-jet recording systems, the piezo-inkjet system involving the discharge of ink by making use of the deformation of a piezoelectric element, and the thermal inkjet system involving the discharge of ink in the form of liquid droplets using the phenomenon of ink boiling under the action of thermal energy, are characterized by high resolution and excellent high-speed printability.
Currently, important problems include high speed and high resolution when printing is performed by an ink-jet printer by impacting ink droplets onto a normal paper or a non-absorptive recording medium such as plastic sheets.
Ink-jet recording involves discharging ink droplets in accordance with an image data, and forming a line or an image with these drops on a recording medium. Particularly, in the case of performing recording on a non-absorptive recording medium as described above, there have been problems in practice, such as that if it takes some time to make ink droplets dry after impact or penetrate into the recording medium, the image is prone to spread, and adjacent ink droplets mix with each other on the recording medium and impair the formation of clear images. When ink droplets mix with each other, ink droplets impacted adjacently to each other unite, thus causing movement of ink droplets. Thus, ink droplets go out from the impact position, and in the case of drawing a thin line, non-uniformity occurs in the line width, and in the case of recording colored planes, color irregularities and the like occur. Furthermore, there has also been a problem that since the non-uniformity of the line width and the extent of the occurrence of color irregularities on colored planes vary with the ink absorbability or wettability of the surface of a recording medium, image changes between various recording medias even though the ink to be used and the conditions for discharge are maintained constant.
As a method of suppressing the spread of images or the non-uniformity of line width, there may be mentioned a method of accelerating the fixation of ink droplets. As an example, a binary liquid type ink having reactivity is used so that the two liquids react with each other on a recording medium, so as to impart high precision drawing properties. For example, a method of attaching a liquid having a basic polymer, and then recording with an ink containing an anionic dye (see, for example, JP-A No. S63-60783); a method of applying a liquid composition containing a cationic material, and then applying an ink containing an anionic compound and a colored material (see, for example, JP-A No. H8-174997); or the like have been disclosed.
Furthermore, there has been proposed an ink-jet recording method comprising using an ultraviolet-curable ink as the ink, irradiating the dots of the ultraviolet-curable color ink discharged on a recording medium with ultraviolet rays according to the respective timing for discharge, preliminarily curing the ink to the extent that adjacent dots have increased viscosities and do not mix with each other, and then further irradiating the dots with ultraviolet rays to cure the dots (see, for example, JP-A No. 2004-42548).
Moreover, there has also been proposed a technology for improving the visibility of color inks, spreading and the problem of images changing between various recording medias, by providing a uniform coating of a radiation-curable white ink as an undercoat layer on a transparent or semi-transparent non-absorbable recording medium, irradiating the white ink with a radiation to solidify the ink or increase the viscosity, and then performing ink-jet recording using a set of radiation-curable color inks (see, for example, JP-A No. 2003-145745 and JP-A No. 2004-42525). Also, a technology for providing a coating of a substantially transparent actinic ray-curable ink, instead of the above-mentioned radiation-curable white ink, by an ink-jet head (see, for example, JP-A No. 2005-96254) has been proposed as well.
On the other hand, as an ultraviolet-curable ink-jet ink composition having good fixability to non-absorptive materials such as plastics or metals, an ultraviolet-curable ink-jet ink composition comprising a phosphorus-based compound is known (see, for example, JP-A No. 2005-126540).
However, with the method described in JP-A No. 2004-42548, spreading is suppressed, but the problem of images changing between various recording medias still remains. Thus, the method is not sufficient for eliminating the problems of non-uniformity in line width or color irregularities, which is caused by the intermixing of ink droplets. Furthermore, the methods described in JP-A No. 2003-145745 and JP-A No. 2004-42525 are also insufficient for eliminating the problems of non-uniformity in line width or color irregularities, which is caused by the intermixing of ink droplets. Moreover, the method described in JP-A No. 2005-96254 also holds the problems of non-uniformity in line width or color irregularities, which is caused by the intermixing of ink droplets.
On the other hand, in an ink-jet image forming system, since color inks are sequentially applied on a base material during image formation, there occur cases where an ink to be applied later is applied on an ink that has been applied previously, and cases where a color ink is applied on a site where ink has been applied. In the respective cases, there is a problem that if the dot diameter (and the dot shape) changes, deterioration of images occur.
Further, in the case of recording images using the ultraviolet-curable ink-jet ink composition described in JP-A No. 2005-126540, since an undercoat solution is not used, there is a problem that mixing of colors occur, or reproducibility of dots cannot be obtained.
On the other hand, in the single-pass system which is capable of high speed image formation such as in the case of recording images using a low resolution head unit, when the amount of ink droplets impacting the medium is small, or the ink droplet impact density during recording is low, the ink droplets (dots) may spread out disorderly to cause smudged images or blurred images. Or to the contrary, dots may not sufficiently spread out, thereby causing problems such as decoloration, decrease of image density, blurring of images, and color irregularities.